Radio communication spectrums are valuable natural resources. With rapid development of the wireless communication technologies, spectrum resources are increasingly scarce. In order to ease the strain on the spectrum resources, relevant departments and agencies have monitored and studied the wireless communication spectrums, and found that some frequency bands (such as a frequency band for television) are not used in most of time or not used within most areas, while multi-user or multi-system contention occurs in some other frequency bands. In other words, some systems with heavy service loads do not have sufficient spectrum resources, while other systems with small service loads take up too many resources. The concept of CR emerges under this background. The basic principle of CR is described as follows. Under the premise of not interfering an authorization system, a CR system may dynamically select a white space frequency for communication through monitoring changes of a current wireless environment.
When the CR system opportunistically uses the white space frequency of the authorization system, a basic premise is to protect the authorization system from interference. The protection mainly includes two aspects. One aspect is that the CR system may accurately determine which frequency of the authorization system is an available white space frequency (introduction of the CR system on this frequency may not affect normal work of the authorization system). The other aspect is that when an occupied frequency is no longer available, the CR system may timely return the occupied frequency to the authorization system.
There are mainly two methods for detecting a white space frequency. The first method is a database method, in which through accessing an information database of the authorization system, the CR system obtains using information about frequencies of an authorization system in a certain area, and further determines which frequency is free and available. The second method is a sensing/detecting method, in which a sensing/detecting module of the CR system detects authorization system signals on different frequencies. When it is detected that an input parameter is greater than a threshold, the sensing/detecting module determines that an authorization system signal exists on a frequency and the frequency is not available to the CR system. Otherwise, the frequency is available to the CR system.
There are three typical sensing algorithms (or referred to as detection algorithms) for detecting an authorized signal, i.e., energy detection, matched filter detection, and self-correlation detection. To achieve a certain detecting performance, any of the sensing algorithms has requirements on receiving and collecting time of a signal and a receiving carrier interference ratio of the signal.
However, during the sensing detecting, since the CR system is also working on an authorized frequency, a signal of the CR system may interfere the sensing detecting on the authorization system signal. A commonly-used method is to configure a quiet period (also referred to as silence period). In this case, during the sensing detecting, the CR system stops sending any data on a corresponding frequency within the quiet period, so as to ensure that the frequency is not interfered. A typical quiet period mainly includes parameters such as a period cycle, the offset within the period cycle, and the duration of the quiet period, etc. FIG. 1 is a schematic flowchart illustrating a process for configuring the quiet period. As shown in FIG. 1, when a quiet period parameter is defined, the quiet period parameter is sent to a terminal.
As can be seen that the more frequently the sensing detecting is performed, i.e., the more frequent the quiet is, the greater the chance for discovering the authorization system is, the more timely the operation of exiting the frequency of the authorization system is performed, and the smaller the interference to the authorization system is. However, if the duration of the quiet period of the CR system is too long or the quiet is performed too often, the capacity of the CR system may be greatly affected, therefore there is no sense in using the white space frequency to improve the system capacity.
Previous studies on the quiet period focus on how to configure and transfer the quiet period parameter among multiple terminals. However, the value of the quiet period parameter not only affects the interference to the authorization system and the capacity of the sensing system, but also affects the selection of the sensing algorithm, thereby affects the hardware complexity when the system is implemented. As such, the quiet period parameter may be reasonably configured, so as to reduce the interference to the authorization system and control the loss of the CR system.